Sliding member

ABSTRACT

A sliding member for a journal bearing is provided. A sliding layer includes fibrous particles dispersed in a synthetic resin, and has a sliding surface side region and an interface side region. The particles have an average particle size D sur, axi  and D sur, cir  respectively in an axial and circumferential cross-section in the sliding surface side region, and D int, axi  and D int, cir  respectively in axial and circumferential cross-sections in the interface side region. D sur, axi  and D int, cir  are 5-30 μm, and D sur, cir  and D int, axi  are 5 to 20% of respectively D sur, axi  and D int, cir . A dispersion index of the particles having the major axis length of 20 μm or longer is 5 or more, both in the sliding surface side region in view of the axial cross-section and in the interface side region in view of the circumferential cross-section.

FIELD OF THE INVENTION

The present invention generally relates to a sliding member for a journal bearing. Specifically, it relates to a sliding member having a partial cylindrical shape and including a back-metal layer, and a sliding layer including synthetic resin and fibrous particles. The present invention further relates to a journal bearing including the sliding member.

DESCRIPTION OF RELATED ART

A radial bearing has been used as a journal bearing for a rotation shaft of an exhaust turbine, a large-scale electrical generator or other devices. The radial bearing includes a plurality of sliding members having a bearing pad shape with a circular-arc cross section, which are arranged around a rotation shaft (see e.g. JP 2004-156690A). As the sliding member for the radial bearing, a sliding member including a resin sliding layer coated on a back metal layer has been known. JP 10-204282A and JP 2016-079391A disclose a resin composition including fibrous particles, such as glass fibrous particles, carbon fibrous particles or intermetallic compound fibrous particles, dispersed in the synthetic resin to increase strength of the sliding layer. JP 2013-194204A discloses to disperse fibrous particles in a resin matrix in a non-oriented or isotropic manner, to prevent the fiber-reinforced resin composition from having anisotropy of strength. In JP 2018-146059A, fibrous particles are dispersed so as to orient substantially parallel to the sliding layer in a surface side region and an interface side region of the sliding layer while the particles in an intermediate region of the sliding layer are oriented substantially perpendicular to the sliding layer, thereby preventing damages such as cracks on a surface of the sliding layer when a bearing device starts its operation.

BRIEF SUMMARY OF THE INVENTION

During steady operation of an exhaust turbine, a large-scale electrical generator or other devices, a fluid lubricating film, such as oil film, is formed between a surface of a shaft member and a sliding surface of a sliding member, thereby a direct contact between the shaft member and the sliding member is prevented. However, in the stopping time period thereof, supply of such as oil is stopped, and thus the shaft continues to rotate for a certain time without the supply of the fluid lubricating film of oil or the like before the rotation is completely stopped. Accordingly, the shaft member slides against the sliding surface of the sliding member while the shaft member is in direct contact with the sliding surface of the sliding member. When the shaft member slides against the sliding surface of the sliding member in this way, a resin composition near the sliding surface in contact with the shaft member is drawn by the shaft member and elastically deformed in a rotation direction of the shaft member. In this case, if fibrous particles are dispersed in the sliding layer in a non-oriented manner, i.e., in an isotropic manner as in JP 2013-194204A, the fibrous particles in the vicinity of the sliding surface is largely deformed, and are more likely to fall off, leading to wear of the sliding layer. Thus, damages such as cracks are more likely to occur on the surface of the sliding layer. The same applies when the fibrous particles are dispersed in the sliding layer such that more fibrous particles have major axes oriented perpendicular to the sliding surface. On the other hand, when the fibrous particles are dispersed in the sliding layer such that the more fibrous particles have major axes oriented substantially parallel to the sliding surface, the elastic deformation of the resin composition in the rotation direction of the shaft member is small. However, the fibrous particles in the vicinity of the sliding surface are more likely to fall off, leading to a large amount of wear of the resin composition near the sliding surface. Thus, damages such as cracks are more likely to occur. As stated in JP 2018-146059A, when the fibrous particles are dispersed in the sliding layer such that the fibrous particles in a surface side region and an interface side region of the sliding layer are oriented substantially parallel to the sliding layer and the fibrous particles in an intermediate region of the sliding layer are oriented substantially perpendicular to the sliding layer, the generation of damage such as cracks on the surface of the sliding layer is prevented when the bearing device starts to operation. When the bearing device is in the stopping period, however, a larger load is applied to the sliding surface of the sliding member. Accordingly, if the shaft continues to rotate in direct contact with the sliding surface of the sliding member for a certain time without the supply of the fluid lubricating film of oil or the like, the fibrous particles near the sliding surface possibly fall off. This causes another problem that damages such as cracks are more likely to occur on the surface of the sliding layer.

An object of the present invention is to overcome the above problems of the prior arts and provide a sliding member that is less likely suffer from damage such as cracks on a surface of a sliding layer when a bearing device is in the stopping period.

According to an aspect of the present invention, provided is a sliding member for a journal bearing. The sliding member includes a back-metal layer and a sliding layer on the back-metal layer. The sliding member has a partial cylindrical shape. The sliding layer includes a synthetic resin, and fibrous particles dispersed in the synthetic resin at a volume ratio of 10 to 35% of the sliding layer. The sliding layer is composed of a sliding surface side region including a sliding surface of the sliding layer, and an interface side region including an interface between the sliding layer and the back-metal layer. A thickness of the interface side region is 15 to 50% of a thickness of the sliding layer (from the interface between the sliding layer and the back-metal layer toward the sliding surface). In the sliding surface side region, the fibrous particles have a first average particle size D_(sur, axi) of 5 to 30 μm in view of an axial cross-section, and have a second average particle size D_(sur, cir) in view of a circumferential cross-section. The second average particle size D_(sur, cir) is 5 to 20% of the first average particle size D_(sur, axi). In the interface side region, the fibrous particles have a third average particle size D_(int, cir) of 5 to 30 μm in view of a circumferential cross-section, and have a forth average particle size D_(int, axi) in view of an axial cross-section. The forth average particle size D_(int, axi) is 5 to 20% of the third average particle size D_(int, cir).

In the sliding surface side region in view of the axial cross-section, the fibrous particles therein includes fibrous particles having a length of a major axis of not shorter than 20 μm, and a volume ratio of the fibrous particles having the major axis length of not shorter than 20 μm to a total volume of the fibrous particles in the sliding surface side region is not less than 10%. Furthermore, a dispersion index of the fibrous particles having the major axis length of not shorter than 20 μm is not less than 5.

In the interface side region in view of the circumferential cross-section, the fibrous particles therein includes fibrous particles having a length of major axis of not shorter than 20 μm, and a volume ratio of the fibrous particles having the major axis length of not shorter than 20 μm to a total volume of the fibrous particles in the interface side region is not less than 10%. A dispersion index of the fibrous particles having the major axis length of not shorter than 20 μm is not less than 5.

Here, the dispersion index is defined as an average of ratios X1/Y1 of the fibrous particles, where X1 represents a length of a fibrous particle in a cross-section in a direction parallel to the sliding surface, and Y1 represents a length of a fibrous particle in the cross-section in a direction perpendicular to the sliding surface.

According to an embodiment of the present invention, in the sliding surface side region of the axial cross-section, an average aspect ratio of the fibrous particles having the major axis length of not shorter than 20 μm is preferably 1.5 to 10, and more preferably 5 to 10. Furthermore, in the interface side region of the circumferential cross-section, an average aspect ratio of the fibrous particles having the major axis length of not shorter than 20 μm having the major axis length of not shorter than 20 μm is preferably 1.5 to 10, and more preferably 5 to 10.

According to an embodiment of the present invention, in the sliding surface side region of the axial cross-section, the volume ratio of the fibrous particles having the major axis length of not shorter than 20 μm to the total volume of the fibrous particles in the sliding surface side region is preferably not less than 30%. Furthermore, in the interface side region of the circumferential cross-section, a volume ratio of the fibrous particles having the major axis length of not shorter than 20 μm to the total volume of the fibrous particles in the interface side region is preferably not less than 30%.

According to an embodiment of the present invention, the fibrous particles are preferably composed of one or more selected from glass fiber particles, ceramic fiber particles, carbon fiber particles, aramid fiber particles, acrylic fiber particles, and polyvinyl alcohol fiber particles.

According to an embodiment of the present invention, the synthetic resin is preferably composed of one or more selected from polyether ether ketone, polyether ketone, polyether sulfone, polyamidimide, polyimide, polybenzimidazole, nylon, phenol, epoxy, polyacetal, polyphenylene sulfide, polyethylene, and polyetherimide.

According to an embodiment of the present invention, the sliding layer preferably further includes one or more solid lubricants selected from graphite, molybdenum disulfide, tungsten disulfide, boron nitride, and polytetrafluoroethylene.

According to an embodiment of the present invention, the sliding layer preferably further includes 1 to 10 volume % of one or more fillers selected from CaF₂, CaCo₃, talc, mica, mullite, iron oxide, calcium phosphate, potassium titanate, and Mo₂C (molybdenum carbide).

According to an embodiment of the present invention, the back-metal layer preferably includes a porous metal portion on a surface which is the interface between the back-metal layer and the sliding layer.

According to another aspect of the present invention, provided is a journal bearing including a plurality of the above sliding members.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an axial cross section of a sliding member according to an embodiment of the present invention.

FIG. 1A is an enlarged view of a sliding layer side region of a sliding layer of the sliding member in FIG. 1.

FIG. 1B is an enlarged view of an interface side region of the sliding layer of the sliding member in FIG. 1.

FIG. 2 shows a circumferential cross section of a sliding member according to an embodiment of the present invention.

FIG. 2A is an enlarged view of a sliding layer side region of a sliding layer of the sliding member in FIG. 2.

FIG. 2B is an enlarged view of an interface side region of the sliding layer of the sliding member in FIG. 2.

FIG. 3 shows a view for explaining an aspect ratio (A) of a fibrous particle.

FIG. 4 shows a view for explaining a dispersion index (S) of a fibrous particle.

FIG. 5 shows an axial cross section of a sliding member according to another embodiment of the present invention.

FIG. 6 shows a circumferential cross section of a sliding member according to another embodiment of the present invention.

FIG. 7A shows a view for explaining a flow of resin.

FIG. 7B shows a A-A cross section in FIG. 7A.

FIG. 8 is a schematic diagram of an example of the sliding member according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 8 schematically depicts a partially cylindrical shaped sliding member 1 according to an embodiment of the present invention. The sliding member 1 has a shape of a partial cylinder. The partial cylinder is defined as a part obtained by cutting a cylinder along an axial direction (L direction) of the cylinder. An inner surface of the sliding member 1 constitutes a sliding surface for sliding against a shaft member during operation as a bearing. The sliding member 1 therefore includes a back metal layer 2 on an outer surface side, and a sliding layer 3 on an inner surface of the back metal layer 2. A sliding surface 30 corresponds to the inner surface of the sliding layer 3 and forms a concave curved surface. The sliding surface 30 has curvature designed to match with that of the opposed shaft member.

A circumferential direction of the cylindrical shape is referred to as a “circumferential direction” (C direction), that is a direction in which the partially cylindrical sliding member has a maximum curvature. An axial direction of the cylindrical shape is referred to as an “axial direction” or a “longitudinal direction” (L direction), that is a direction in which a straight line can be drawn on the partially cylindrical sliding member. The shaft member slides in the “circumferential direction” when it is used as a bearing. Thus the “circumferential direction” corresponds to a sliding direction.

FIG. 1 schematically shows an axial cross section of the sliding member 1 according to an embodiment of the present invention. The axial cross section is cut along a direction perpendicular to the sliding surface 30 and along the axial direction of the sliding layer 3. FIG. 2 schematically shows a circumferential cross section of the sliding member 1 according to an embodiment of the present invention. The circumferential cross section is cut along a direction perpendicular to the sliding surface 30 and along the circumferential direction of the sliding layer 3.

The sliding member 1 includes a sliding layer 3 on a back-metal layer 2. The sliding layer 3 includes 10 to 35 volume % of fibrous particles 5 dispersed in a synthetic resin 4. The sliding layer 3 is composed of a sliding surface side region 31 on a side including the sliding surface 30, and an interface side region 32 on a side including an interface 7 between the sliding layer 3 and the back-metal layer. A thickness of the interface side region 32 is 15 to 50% of a thickness of the sliding layer 3. In each region 31, 32, 10 to 35 volume % of fibrous particles 5 are preferably dispersed in the synthetic resin 4. More fibrous particles 5 in the sliding surface side region 31 are orientated such that major axes thereof are orientated substantially parallel to the axial direction of the sliding surface 30 (see FIGS. 1A and 2A), and more fibrous particles 5 in the interface side region 32 are orientated such that major axes thereof are orientated substantially parallel to the circumferential direction of the sliding surface 30 (see FIGS. 1B and 2B). That is, the orientation of the fibrous particles in the sliding surface side region 31 and that in the interface side region 32 are approximately orthogonal to each other (in the axial direction and the circumferential direction). Please note that the orientations of the fibrous particles in the sliding surface side region 31 and in the interface side region 32 are both approximately parallel to the sliding surface 30.

Here, when an average particle size of the fibrous particles in the sliding surface side region of the axial cross-section is represented by “D_(sur, axi)”; that in the sliding surface side region of the circumferential cross-section is represented by “D_(sur, cir)”; that in the interface side region of the axial cross-section is represented by “D_(int, axi)”: and that in the interface side region of the circumferential cross-section is represented by “D_(int, cir)”, they satisfy following relations.

D_(sur, axi) is 5 to 30 μm, and D_(sur, cir) is 5 to 20% of D_(sur, axi), and

D_(int, cir) is 5 to 30 μm, and D_(int, axi) is 20% of D_(int, cir).

The average particle sizes D_(sur, axi) and D_(int, cir) are determined to be 5 to 30 μm for the following reason. When the average particle sizes are smaller than 5 μm, an effect of increasing strength (resistance to deformation) of the sliding layer 3 decreases. When the size exceeds 30 μm, shear is easily generated in the fibrous particles 5 under a load applied to the sliding layer 3 from the shaft member.

The volume ratio of the fibrous particles 5 in the sliding layer 3 of the sliding member 1 is determined as 10 to 35% for the following reason. When the ratio is smaller than 10%, strength (resistance to deformation) of the sliding layer 3 decreases. When the ratio exceeds 35%, the sliding layer 3 becomes brittle and thus an amount of wear easily increases during sliding.

When the axial cross-section of the sliding member 1 is observed, the sliding surface side region 31 includes fibrous particles which have a length of a major axis being not shorter than 20 μm, and such fibrous particles are included by not less than 10 volume % relative to a total volume of the fibrous particles in the sliding surface side region 31. This volume ratio is preferably not less than 30%. On the other hand, when the circumferential cross-section of the sliding member 1 is observed, the interface side region 32 includes fibrous particles which have a length of a major axis being not shorter than 20 μm, and such fibrous particles are included by not less than 10 volume % of relative to a total volume of the fibrous particles in the interface side region 32. This volume ratio is also preferably not less than 30%. Here, the “length of the major axis” is defined as a length of the fibrous particle in a direction in which the fibrous particles have a maximum length in the cross-section. The fibrous particles having the length of the major axis being not shorter than 20 μm have a large effect of increasing strength, i.e., resistance to deformation, of the sliding layer 3. When the sliding layer includes not less than 10 volume % of “fibrous particles having the length of the major axis being not shorter than 20 μm” relative to the total volume of the fibrous particles, high strength or resistance to deformation can be obtained in in a direction where such fibrous particles are oriented in the sliding surface side region 31 and the interface side region 32

The synthetic resin 4 is preferably one or more selected from polyether ether ketone, polyether ketone, polyether sulfone, polyamide imide, polyimide, polybenzimidazole, nylon, phenol, epoxy, polyacetal, polyphenylene sulfide, polyethylene, and polyether imide. The fibrous particles 5 are preferably one or more selected from glass fibrous particles, ceramic fibrous particles, carbon fibrous particles, aramid fibrous particles, acrylic fibrous particles, and polyvinyl alcohol fibrous particles. However, the synthetic resin 4 and the fibrous particles 5 may be of other materials.

The sliding layer 3 may further include one or more solid lubricants selected from graphite, molybdenum disulfide, tungsten disulfide, boron nitride, and polytetrafluoroethylene. The solid lubricant/lubricants can improve sliding properties of the sliding layer 3. The sliding layer 3 may further include 1 to 10 volume % of one or more fillers selected from CaF₂, CaCo₃, talc, mica, mullite, iron oxide, calcium phosphate, potassium titanate, and Mo₂C (molybdenum carbide). The filler/fillers can improve wear resistance of the sliding layer 3.

The sliding layer 3 preferably has a thickness of 0.5 to 6 mm, where the thickness of the sliding member is defined as a distance from the sliding surface 30 to the interface 7 between the sliding layer 3 and the back metal layer 2 in a direction perpendicular to the sliding surface 30.

In the axial cross-section, a dispersion index S of the “fibrous particles 5 which have the major axis length of not shorter than 20 μm” dispersed in the sliding surface side region 31 is not less than 5. Furthermore, in the circumferential cross-section, a dispersion index S of the “fibrous particles 5 which have the major axis length of not shorter than 20 μm” dispersed in the interface side region 32 is not less than 5. The dispersion index S is defined as an average ratio X1/Y1 of the fibrous particles 5. Here, “X1” represents a length of the fibrous particles 5 in a direction parallel to the sliding surface 30 in an object cross-section (i.e. axial cross-section or circumferential cross-section), and “Y1” represents a length of the fibrous particles 5 in a direction perpendicular to the sliding surface 30 in the axial cross-section or the circumferential cross-section (see FIG. 4).

The dispersion index S of the fibrous particles 5 is not less than 5 in the sliding surface side region 31 of the sliding layer 3 in the axial cross-section. The value of the dispersion index indicates that a large percentage of the fibrous particles 5 are orientated such that the major axis thereof is directed along the sliding surface 30 and in the axial direction. Thus, the sliding surface side region 31 therefore exhibits such an anisotropic property that it has higher strength (high resistance to deformation) to a load applied parallel to the sliding surface 30 and in the axial direction.

On the other hand, the dispersion index S of the fibrous particles 5 is not less than 5 in the interface side region 32 of the sliding layer 3 in the circumferential cross-section. A large percentage of the fibrous particles 5 are orientated such that the major axis thereof is directed along the sliding surface 30 and in the circumferential direction in the interface side region 32. Accordingly, the interface side region 32 of the sliding layer 3 has higher strength (high resistance to deformation) against a load applied parallel to the sliding surface 30 and in the circumferential direction.

Since the fibrous particles 5 are oriented in this manner, even if the shaft member slides for a certain time period in direct contact with the sliding surface 30 of the sliding layer 3 in a stopping time period of the bearing device, fibrous particles 5 is less deformed and shear is less likely to generate. It is because the fibrous particles are oriented parallel to the sliding surface 30 and in the axial direction in the sliding surface side region 31 including the sliding surface 30, and the resistance to deformation in the circumferential direction is low. Even when the fibrous particles are drawn by the shaft member, the fibrous particles are displaced (moved) while held by the synthetic resin 4, and thus fibrous particles 5 is less deformed. Therefore, the fibrous particles are less likely to fall off of from the sliding surface 30 and the wear is less likely to generate, thereby preventing cracks on the sliding surface 30.

On the other hand, in the interface side region 32 of the sliding layer 3, the fibrous particles are oriented parallel to the sliding surface 30 and in the circumferential direction, and thus the resistance to deformation in the circumferential direction is higher than in the sliding surface side region. Accordingly, the deformation in the circumferential direction of the interface side region 32 is small against a load of the shaft member applied to the sliding layer 3. Thus, shear is less likely to be caused by a difference of amount of elastic deformation between the back-metal layer 2 and the resin composition in contact with the back-metal layer 2.

Through the above mechanism, the sliding member 1 of the present invention is prevented from generation of damages such as cracks on the surface of the sliding layer 3, even though the sliding surface 30 is in direct contact with a surface of a counter shaft during the stopping period of the bearing device.

The sliding surface side region 31 and the interface side region 32 of the sliding layer may include approximately the same amount of fibrous particles, and they may include approximately the same amount of “fibrous particles which have the major axis length of not shorter than 20 μm”. Furthermore, the dispersion indexes of the “fibrous particles which have the major axis length of shorter than 20 μm” dispersed in the sliding surface side region 31 and the interface side region 32 of the sliding layer may be approximately the same as the dispersion indexes of the “fibrous particles which the major axis length of not shorter than 20 μm” dispersed in the sliding surface side region 31 and the interface side region 32, respectively.

In the sliding surface side region of the axial cross-section, an average aspect ratio of the “fibrous particles which have the major axis length of not shorter than 20 μm” is preferably 1.5 to 10, more preferably 5 to 10, and still more preferably 7 to 10. In the interface side region of the circumferential cross-section, an average aspect ratio of the “fibrous particles which have the major axis length of not shorter than 20 μm” is preferably 1.5 to 10, more preferably 5 to 10, and still more preferably 7 to 10. The average aspect ratio relates to orientation of the fibrous particles. When the major axes of the fibrous particles are not oriented substantially parallel to a cross section (in the axial direction or the circumferential direction) to be observed, the aspect ratio is close to 1 (e.g., less than 1.5). If the average aspect ratio is less than 1.5, the effect of increasing the strength (resistance to deformation) of the resin layer is reduced. In this case, even if the “fibrous particles which have the major axis length of not shorter than 20 μm” have different orientations between the sliding surface side region and the interface side region, a difference in anisotropy of the deformation resistance is more likely to be insufficient, and thus the above effect is less likely to be obtained. On the other hand, if the average aspect ratio is more than 10, fibrous particles may be sheared under a load applied from the shaft member to the sliding layer.

The back metal layer 2 may include a porous metal portion 6 on its surface that is an interface between the back metal layer 2 and the sliding layer 3. FIGS. 5 and 6 schematically depict, respectively, axial and circumferential cross sections of the sliding member 1 in an embodiment in which the back metal layer 2 includes the porous metal portion 6. When the porous metal portion 6 is formed on the surface of the back metal layer 2, bonding strength between the sliding layer 3 and the back metal layer 2 increases. More specifically, the porous metal portion 6 increases a bonding force between the back metal layer 2 and the sliding layer 3 by an anchor effect, since a material of the sliding layer 3 impregnates in pores of the porous metal portion 6.

The porous metal portion 6 may be produced by sintering a metal powder such as Cu, Cu alloy, Fe, or an Fe alloy on a surface of a metal plate, a strip or the like. The porous metal portion 6 may have porosity of approximately 20 to 60%. The porous metal portion 6 may have a thickness of approximately 50 to 500 μm. In this case, the sliding layer 3 coated on a surface of the porous metal portion 6 may have a thickness of 0.5 to 6 mm. However, these dimensions are mere examples, and other dimensions may be adopted.

The above sliding member may be used for e.g. a journal bearing (radial bearing). For example, this bearing may include a housing defining a cylindrical inner cavity. The housing is composed of one or more of housing elements, typically two elements. A plurality of the sliding members are arranged on an inner circumferential surface in the inner cavity along a circumferential direction to support a shaft member on the sliding members. The sliding member has a partially cylindrical shape. The shape (e.g., curvature and size) of the sliding members is designed to match with the inner cavity and the shaft member. However, the sliding member may be also used for other bearings or for other sliding applications.

The present invention is also directed to a journal bearing including a plurality of the above sliding members.

A process of manufacturing the above sliding member is described in detailed hereinafter.

(1) Preparation of Fibrous Particle Material

Examples of the material of the fibrous particles include artificially produced inorganic fibrous particles (e.g., glass fibrous particles or ceramic fibrous particles), and organic fibrous particles (e.g., carbon fibrous particles, aramid fibers, acrylic fibrous particles, or polyvinyl alcohol fibrous particles).

(2) Preparation of Synthetic Resin Material Particles

Particles having an average particle size of 7 to 30 μm and an aspect ratio of 5 to 100 are preferable for the synthetic resin material. The synthetic resin may be one or more selected from polyether ether ketone, polyether ketone, polyether sulfone, polyamide imide, polyimide, polybenzimidazole, nylon, phenol, epoxy, polyacetal, polyphenylene sulfide, polyethylene, and polyether imide.

(3) Manufacture of Resin Composition Sheet

A resin composition sheet is produced from the above materials or other with use of a melt-kneading machine, a supply mold, a sheet forming mold, and cooling rolls.

“Melt-Kneading Machine”

The melt-kneading machine mixes the synthetic resin material particles, the fibrous particle material, and other optional materials, such as solid lubricant o filler, while heating the materials at a temperature of 230 to 390° C. to produce a resin composition in a molten state. The molten resin composition is extruded from the melt-kneading machine under fixed pressure.

“Supply Mold”

The molten resin composition is extruded from the melt-kneading machine and is constantly supplied to the sheet forming mold via the supply mold in a constant amount. The supply mold has a heater to heat the resin composition passing through the supply mold at 385 to 400° C. to maintain the resin composition in a molten state.

“Sheet Forming Mold”

The resin composition is formed into a sheet shape by the sheet forming mold. The molten resin composition supplied from the supply mold to the sheet forming mold is formed into a sheet shape, and then gradually naturally cooled, while the sheet moves toward an outlet in the sheet forming mold, to form a sheet in a semi-molten state.

“Cooling Roll”

The resin composition sheet in a semi-molten state is drawn from the “sheet forming mold” while being cooled continuously in contact with the cooling roll. The cooling roll is constituted by at least a pair of rolls (upper roll and lower roll) that press the resin composition sheet from upper and lower sides and transfer it. The resin composition sheet after drawn from the cooling roll is in a completely solid state. A temperature of the cooling roll can be controlled by an electric heater incorporated in the roll, and the cooling roll can be driven to rotate controllably by an electric motor. The resin composition sheet has, for example, a thickness of 1 to 7 mm. The resin composition sheet in a solid state is cut into a size matching a size of a back metal used at a coating step described later.

(4) Back Metal

As the back metal layer, a metal plate made of an Fe alloy such as a hypoeutectoid steel or a stainless steel, Cu, a Cu alloy or the like may be used. A porous metal portion may be formed on a surface of the back metal layer, i.e., on the side facing an interface between the back metal layer and the sliding layer. The porous metal portion may have a same composition as the back metal layer. Alternatively, the porous metal portion may have a different composition or may be of different material from the back metal layer.

(5) Coating and Molding Step

The resin composition sheet is bonded to one surface of the back metal layer, or to the porous metal portion of the back metal. Subsequently, the back metal with the resin composition sheet is molded in a shape for use, such as a partial cylinder, by pressing. Then, the back metal are processed or cut to make a thickness of the composition uniform. The molding is performed such that a drawn direction of the resin composition sheet in the sheet forming step becomes a circumferential direction of the partial cylinder. Then, a surface of one side is cut off to have a predetermined thickness.

Structure Control

Next, a structure control method for controlling orientations of the fibrous particles is hereinafter described. The structure control is performed by setting a temperature of the cooling roll in the manufacturing process of the resin composition sheet. Specifically, a temperature of the upper cooling roll is set at a temperature (at 170° C. to 180° C.) higher by approximately 50° C. to 60° C. than a temperature of the lower cooling roll. On the other hand, in a conventional cooling roll, the temperatures of the upper cooling roll and the lower cooling roll have been set at the same temperature (at 110° C. to 130° C.).

The resin composition sheet in a semi-molten state is solidified while being cooled in contact with the cooling roll. Since the temperature of the lower cooling roll is set to be lower than the temperature of the upper cooling roll, a lower surface of the resin composition sheet starts to be solidified earlier. Since the temperature of the upper cooling roll is higher than the temperature of the lower cooling roll, the resin composition in a semi-molten state that has not been completely solidified tends to be accumulated (hereinafter referred to as “resin accumulation”) at an inlet of the upper cooling roll. FIG. 7A schematically shows this state. The resin composition sheet is drawn in a direction (drawing direction 10) from the right side toward the left side of FIG. 7A. Arrow 11 shows a flow of the resin composition in a semi-molten state. The resin composition 11 in a semi-molten state that has flowed from a sheet forming mold 12 (from the right side of FIG. 7A) forms a certain amount of resin accumulation 15 at an inlet of an upper cooling roll 13. The resin composition 11 in a semi-molten state (hereinafter referred to as “semi-molten resin composition”) that forms the resin accumulation 15 is accumulated as being rotated in the same direction as the drawing direction, and the resin composition 11 is pushed into an inside of the resin composition sheet. Since the inside of the resin composition sheet is not in contact with the cooling roll, the resin composition sheet therein maintains in a semi-molten state during the resin composition sheet is passing through the cooling roll. The semi-molten resin composition 11 pushed into the inside of the resin composition sheet collides against a lower surface 16 of the resin composition sheet that has been already solidified by the lower cooling roll 14, and then the semi-molten resin composition 11 spreads and flows toward both ends in a width direction of the resin composition sheet (see FIG. 7B) and starts to be solidified. Thus, near a center portion of the resin composition sheet in a thickness direction, major axes of the fibrous particles are more likely to be oriented in the width direction of the resin composition sheet (i.e., a direction perpendicular to the drawing direction 10). In the vicinity of surfaces of the resin composition sheet (upper and lower surfaces of the sheet), on the other hand, the semi-molten resin composition sheet is constantly flowing in a single direction toward an outlet of the cooling roll and is solidified by the contact with the cooling roll. Thus, major axes of the fibrous particles are more likely to be oriented in a longitudinal direction (drawing direction 10) on the surface of the resin composition sheet.

In a conventional method, the temperatures of the upper cooling roll and the lower cooling roll have been set at the same temperature. In this case, the semi-molten resin composition that has flowed from the sheet forming mold constantly flows in a single direction toward the outlet without forming a resin accumulation at the inlet of the cooling roll. Accordingly, the fibrous particles have the major axis orientated parallel to a surface of the sheet throughout the sheet.

When the resin composition sheet is manufactured by a conventional injection molding, the molten resin composition is injected in a moment from a supply port of the sheet forming mold. In this case, collision and junction of the molten resin composition occur at various positions within the mold. The collision and junction of the resin composition produce different orientations between a portion where the resin composition flows in one direction and a portion where the collision occurs. As a result, the resin composition sheet has a mixture of portions where the fibrous particles are orientated parallel to the surface of the sheet and portions where the fibrous particles are oriented at random (weld portions) as viewed from the surface.

As described in JP-A-2013-194204 where a resin composition sheet is manufactured through an injection molding process from a resin composition including synthetic resin, cross-linking promotor and fibrous particles, the fibrous particles are dispersed in a non-oriented (isotropic) manner.

As disclosed in JP 2018-146059A where a resin composition sheet is manufactured by cooling a resin composition in the forming mold and periodically changing a drawing speed of a cooling roll, fibrous particles are dispersed such that major axes of the fibrous particles are oriented perpendicular to a surface of the sheet in a center region in a thickness direction, while fibrous particles are dispersed such that major axes of the fibrous particles are oriented parallel to the surface of the sheet in the vicinity of the surface of the sheet.

Next, a method of dividing a sliding surface side region and an interface side region are described herein. Electronic images of a plurality of portions of the axial cross section and the circumferential cross section of the sliding member are taken at a magnification of 200 times with use of an electron microscope. In the axial cross section, a large number of elongated fibrous particles oriented approximately along the sliding surface are observed near the sliding surface (see FIG. 1A), while almost no such elongated fibrous particles are observed and most of the fibrous particles are spherical or spheroidal particles near the interface between the sliding layer and the back-metal layer (see FIG. 1B). In the circumferential cross section, on the other hand, almost no elongated fibrous particles are observed and most of the fibrous particles are spherical or spheroidal particles near the sliding surface (see FIG. 2A), and a large number of elongated fibrous particles are observed near the interface between the sliding layer and the back-metal layer (see FIG. 2B). These two regions having different forms of the fibrous particles are observed as two layers laminated in a thickness direction of the sliding layer. Thus, a boundary line between the two regions is determined by observing the plurality of axial and circumferential cross sections, and a virtual (boundary) line UL can be drawn parallel to the sliding surface. A region from the sliding surface to the virtual line UL is defined as the sliding surface side region, and a region from the interface between the sliding layer and the back-metal layer to the virtual line UL is defined as the interface side region. In FIG. 1, the virtual line UL is indicated by a dotted line.

When a porous portion is formed on the surface of the back-metal layer, the surface of the back-metal layer has concave and convex portions. In this case, the interface between the sliding layer and the back-metal layer is indicated by a virtual line that is parallel to the sliding surface and passes through an apex of a convex portion on the surface of the back-metal layer (i.e. porous portion) located closest to the sliding surface in the images.

In each of the cross sections, an average particle size of the fibrous particles in the sliding surface side region and the interface side region is measured by the following method.

Electron images of a plurality of positions in a circumferential cross section and axial cross section of the sliding member are taken with use of the electronic microscope at 200 magnifications. The average particle size of the fibrous particles is obtained by measuring an area of each fibrous particle from the electron images by a typical image analysis method (analysis software: Image-Pro Plus (version 4.5) manufactured by Planetron Inc.), and a diameter of a circle having the measured area is calculated (i.e. equivalent circle diameter) and an average is obtained. However, the magnification is not limited to 200 and other magnification may be used.

Next, measuring of a volume ratio of fibrous particles having the major axis length of not shorter than 20 μm in relation to the total volume of the fibrous particles in the sliding layer is explained below. The fibrous particles in the above images of the sliding surface side region and the interface side region in the axial and circumferential cross sections are classified into a group of fibrous particles having a major axis length of not shorter than 20 μm and a group of the other fibrous particles with use of a typical image analysis method (e.g., analysis software: Image-Pro Plus (version 4.5) manufactured by Planetron Inc.). A total area of all the fibrous particles observed in the images, and a total area of the fibrous particles having a major axis length of not shorter than 20 μm in the images are measured. Thus, a ratio of the total area of the fibrous particles having a major axis length of not shorter than 20 μm in relation to the total area of all fibrous particles is obtained. Please note that this obtained area ratio corresponds to a volume ratio.

The average aspect ratio A is obtained as an average ratio of a major axis length L to a minor axis length S (major axis length L/minor axis length S) of the fibrous particles having a major axis length of not shorter than 20 μm from the electron images taken by the above method (see FIG. 3) The major axis length L of the fibrous particle indicates a length measured in a first direction in which the particle has a maximum length in the electron image, while the minor axis length S indicates a maximum length measured in a second direction perpendicular to the first direction.

The dispersion index S of the fibrous particles is obtained by measuring a length X1 of the fibrous particle having a major axis length of not shorter than 20 μm in the direction parallel to the sliding surface, and the length Y1 of the fibrous particle in the direction perpendicular to the sliding surface, in the sliding surface side region of the axial cross-section and in the interface side region of the circumferential cross-section, and calculating an average ratio of X1/Y1 based on the electron images (see FIG. 4). As the dispersion index S of the fibrous particles indicates a value closer to zero, the dispersed fibrous particles are more oriented in the direction perpendicular to the sliding surface. As the dispersion index S indicates a larger value greater than 5, the major axis is more oriented in the direction parallel to the sliding surface.

EXAMPLES

Examples 1 to 12 of the sliding members including a back-metal layer and a sliding layer according to the present invention and Comparative Examples 21 to 28 were produced in the following manner. Table 1 shows compositions of the sliding layers of the sliding members of Examples and Comparative Examples.

TABLE 1 Fibrous particles Average particle size (μm) Axial Circumferential cross-section cross-section Composition (volume %) Sliding Sliding Cross- surface Interface surface Interface Carbon Glass Linking side side side side Items PEEK PF fiber fiber Gr MoS2 CaF2 promoter region region region region Examples 1 90 — 10 — — — — — 5 0.3 (5%)  0.3 (5%)  5 2 80 — — 20 — — — — 30 5.4 (18%) 5.4 (18%) 30 3 70 — 30 — — — — — 15  3 (20%)  3 (20%) 15 4 75 — 20 — — — 5 — 24 4.3 (18%) 4.3 (18%) 24 5 70 — 25 — — 5 — — 27 5.1 (19%) 5.1 (19%) 27 6 65 — 35 — 5 — 5 — 28 5.3 (19%) 5.3 (19%) 28 7 60 — — 20 — 10  10  — 25 4.8 (19%) 4.8 (19%) 25 8 70 — 15 — 5 — 10  — 25  5 (20%)  5 (20%) 25 9 75 — — 15 — 5 5 — 24 4.8 (20%) 4.8 (20%) 24 10 — 75 — 25 — — — — 5 0.3 (5%)  0.3 (5%)  5 11 70 — 30 — — — — — 14 2.8 (20%) 2.8 (20%) 14 12 70 — 30 — — — — — 16 3.2 (20%)  3 (20%) 15 Comparative 21 70 — — 30 — — — — 3.5 0.5 (13%) 0.5 (13%) 3.5 Examples 22 70 — — 30 — — — — 33 6.6 (20%) 6.6 (20%) 33 23 95 —  5 — — — — — 21  4 (19%)  4 (19%) 21 24 60 — 40 — — — — — 18 3.2 (18%) 3.2 (18%) 18 25 70 — — 30 — — — — 1.5 16.1  26 — 70 25 — — — — 5 2.5 2.5 27 70 — — 30 — — — — 16.1  1.5 28 90 — 20 — — — — — 15  3 (20%)  3 (20%) 15 Fibrous particles Average aspect Dispersion ratio (A) index (S) Volume ratio (%) Axial Circum- Axial Circum- Axial Circum- cross- ferential cross- ferentail cross- ferentail section cross- section cross- section cross- Thickness Sliding section Sliding section Sliding section ratio (%) of Evaluation surface Interface surface Interface surface Interface interface Amount side side side Side side side side Shear at of wear Items region region region region region region region Crack interface (μm) Examples 1 5 1.3 5.0 5.6 11 12 50 absence absence 14.8 2 6.8 3.1 6.3 6.3 26 28 35 absence absence 8.4 3 7.4 3.7 6.4 7.1 26 27 30 absence absence 8 4 9.1 5.4 7.0 6.7 33 34 15 absence absence 6.3 5 10 6.3 7.2 7.3 37 39 20 absence absence 6.7 6 10.9 7.2 7.6 7.4 39 41 15 absence absence 5.4 7 13.1 9.4 6.6 7.0 31 33 20 absence absence 6.1 8 13.7 10 7.1 6.8 31 32 15 absence absence 6 9 9.6 5.9 7.4 6.3 37 39 20 absence absence 6.6 10 5.4 1.7 5.4 5.2 10 11 45 absence absence 13.8 11 7.2 3.6 6.5 6.9 25 26 25 absence absence 7.9 12 7.3 3.5 6.6 7.2 26 25 25 absence absence 8.2 Comparative 21 5 1.3 5.2 5.6  5  7 15 presence presence 41.3 Examples 22 6.8 3.1 5.3 5.1 21 24 15 presence presence 30.6 23 6.8 3.1 5.1 5.1 24 25 15 presence presence 35.9 24 7.4 3.7 6.2 7.1 24 27 15 presence presence 29.4 25 — 10.1 — 8.1 — 95 15 presence absence 24.6 26 5.1 5.2 1.1 1.3 11 10 — presence presence 45.7 27 10.1 — 8.1 — 95 — 15 absence presence 19.3 28 7.1 3.2 6.2 6.2 27 28 10 absence presence 9.1

Material particles for the fibrous particles used in Examples 1 to 12 and Comparative Examples 21 to 28 in Table 1 have an average particle size of 7 to 35 μm, and an average aspect ratio (major axis length/minor axis length) of 5 to 100.

The material for the synthetic resin used in Examples 1 to 12 and Comparative Examples 21 to 28 were polyether ether ketone (PEEK) particles or phenol (PF) particles. These particles had an average size of 125% of that of the material of the fibrous particles.

The material particles for the solid lubricant (MoS₂, Gr) used in Examples 5 to 9 have an average size of 30% of that of the material of the fibrous particles, while the material particles for the filler (CaF₂) have an average size of 25% of that of the material of the fibrous particles. The material particles for the cross-linking promotor used in Comparative Example 26 have an average size of 25% of that of the material of the fibrous particles.

The above materials were mixed at a composition ratio in Table 1, and the compositions were pressed in pellets. The pellets were charged into a melt-kneading machine, and sequentially passed through a supply mold, a sheet forming mold, and a cooling roll to produce a resin composition sheet. For Examples 1 to 9, 11 and 12 and Comparative Examples 21 to 25, 27 and 28, a heating temperature of the melt-kneading machine was set at 350 to 390° C., and for Example 10 the heating temperature was set at 230 to 250° C. With regard to a temperature of the cooling roll for Examples 1 to 12 and Comparative Examples 21 to 24, a temperature of an upper cooling roll was set at 180° C., and a temperature of a lower cooling roll was set at 130° C. For Comparative Examples 25 and 27, the temperatures of the upper and lower cooling rolls were set at the same temperature. For Comparative Example 28, the temperature of the upper cooling roll was set at 200° C. and the temperature of the lower cooling roll was set at 100° C. For Comparative Example 26, a resin composition sheet was produced by injection molding as disclosed in JP 2013-194204A.

Subsequently, the produced resin composition sheet was coated on one of surfaces of the back-metal layer made of an Fe alloy, and then processed into a partial cylindrical shape, which was then cut so that the composition on the back metal layer has a predetermined thickness. While the back metal layer of Examples 1 to 9, 11 and 12 and Comparative Examples 21 to 28 was made of an Fe alloy, that of Example 10 includes a porous sintered portion made of a Cu alloy on a surface of the back-metal layer made of an Fe alloy. For the sliding members of Examples 1 to 12 and Comparative Examples 21 to 25 and 28, a drawing direction of the resin composition sheet through cooling rolls in the sheet forming step was parallel to a circumferential direction of the partial cylindrical shape. In Comparative Example 27, the drawing direction of the resin composition sheet was parallel to an axial direction of the partial cylindrical shape.

The sliding layer of the produced sliding members of Examples 1 to 12 and Comparative Examples 21 to 28 had a thickness of 3 mm, and the back-metal layer had a thickness of 10 mm. In Examples 1 to 12 and Comparative Examples 21 to 24 and 28, a surface portion, where fibrous particles were oriented in a sliding direction on a sliding surface side, was cut so that the sliding layer had a thickness of 3 mm.

An average particle size of the fibrous particles dispersed in each of a sliding surface side region and an interface side region of Examples and Comparative Examples are measured in an axial cross-section and a circumferential cross-section as explained above and the results were shown in the column “average particle size” in Table 1. Also, an average aspect ratio (A) of the “fibrous particles having a major axis length of not shorter than 20 μm” was measured in the sliding surface side region of the axial cross-section and the interface side region of the circumferential cross-section as explained above and the results were shown in the column “average aspect ratio (A)” in Table 1. A dispersion index (S) of the “fibrous particles having a major axis length of not shorter than 20 μm” dispersed in the sliding surface side region of the axial cross-section and the interface side region of the circumferential cross-section was measured as the above and the results were shown in the column “dispersion index (S)” in Table 1. Furthermore, a volume ratio of the fibrous particles having a major axis length of not shorter than 20 μm in relation to the total volume of the fibrous particles dispersed in the sliding layer was measured in the sliding surface side region of the axial cross-section and the interface side region of the circumferential cross-section and the results were shown in the column “volume ratio” in Table 1. The column “thickness ratio (%) of interface side region” in Table 1 shows a ratio of a thickness of the interface side region relative to a thickness of the sliding layer.

A plurality of the sliding members in a shape of a partial cylinder were combined into a cylindrical shape and a sliding test was conducted under conditions in Table 2. The conditions simulate a sliding state where operation of a bearing device is in the stopping period, and a shaft member rotates for a certain time with insufficient oil supply. An amount of wear of the sliding layer after the sliding test for Examples and Comparative Examples were shown in the column “amount of wear (μm)” in Table 1. The surface of the sliding layer was detected at a plurality of positions with a roughness tester to evaluate if any defects were generated after the sliding test for Examples and Comparative Examples. The column “Crack” in Table 1 indicates “presence” when a defect having a depth of not less than 5 μm was measured on the surface of the sliding layer, or “absence” when no defect was measured. A test piece after the sliding test was cut in the direction parallel to the circumferential direction of the sliding member and perpendicular to the sliding surface to check if any shear occurred at the interface between the sliding layer and the back metal with an optical microscope. The column “shear at interface” in Table 1 indicates “presence” when the “shear” was detected at the interface, or “absence” when no “shear” was detected.

TABLE 2 Testing machine Journal sliding tester Load 50 MPa Rotation speed 300 rpm Operation time period 30 minutes Oil VG46 Oil feeding rate 10 cc/minute Oil feeding temperature 50° C. Opposed shaft SUJ2 Roughness of opposed shaft 0.2 Ra

As seen from the results shown in Table 1, an amount of wear after the sliding test of Examples 1 to 12 was smaller than that of Comparative Examples 21 to 26. Particularly, the wear was considerably reduced in Examples 4 to 9, an average aspect ratio (A) of the fibrous particles of which is 5 to 10. The wear of Examples 4 to 9 was smaller than that of Examples 1 to 3, 11 and 12, since Examples 4 to 9 have the volume ratio of the fibrous particles 5 which have “the major axis length of not shorter than 20 μm” being not less than 30% in both of the sliding surface side region of the axial cross-section and the interface side region of the circumferential cross-section, while Examples 1 to 3, 11 and 12 have the volume ratio of less than 30%. It is considered that strength (resistance to deformation) of the sliding layer is more increased as described above.

Furthermore, no crack on the surface of the sliding layer and no shear at the interface were detected after the sliding test in each of Examples of the invention. It is considered that cracking was prevented by the orientations of the fibrous particles in the sliding surface side region and the interface side region as described above.

In contrast, when the fibrous particles in the sliding layer were oriented in the same direction (oriented in a direction parallel to the sliding surface and in the circumferential direction) between the sliding surface side region and the interface side region as in Comparative Example 25, the fibrous particles fall off of on the sliding surface, and thus wear of the sliding layer was more likely to occur and causes cracks on the surface of the sliding layer.

In Comparative Example 27, the fibrous particles in the sliding layer were oriented in the same direction (oriented in a direction parallel to the sliding surface and in the axial direction) between the sliding surface side region and the interface side region. In the case, the strength in the circumferential direction of the entire sliding layer is low and thus causes a large amount of deformation in the circumferential direction, leading to shear at the interface between the sliding layer and the back metal.

In Comparative Example 21, the fibrous particles in the sliding layer side region and the interface side region of the sliding layer had an average particle size of less than 5 μm. Accordingly, an effect of increasing the strength (resistance to deformation) of the sliding layer was small and thus it is considered to have caused a large amount of wear of the sliding layer, cracks on the surface of the sliding layer and shear at the interface between the sliding layer and the back metal.

In Comparative Example 22, the fibrous particles in the sliding layer side region and the interface side region of the sliding layer had a large average particle size of 30 μm. Accordingly, when a load of the shaft member was applied to the sliding layer, shear was more likely to occur in the fibrous particles and thus falling off of the fibrous particles occurred. It is considered to have caused a large amount of wear of the sliding layer, cracks on the sliding surface, and shear at the interface between the sliding layer and the back metal.

In Comparative Example 23, the volume ratio of the fibrous particles in the sliding layer side region and the interface side region of the sliding layer was less than 10%. Accordingly, the sliding layer had low strength (resistance to deformation) and is considered to have caused a large amount of wear of the sliding layer, cracks on the sliding surface, and shear at the interface between the sliding layer and the back metal.

In Comparative Example 24, the volume ratio of the fibrous particles in the sliding layer side region of the sliding layer was more than 35%. Accordingly, the sliding layer was brittle and is considered to have caused a large amount of wear of the sliding layer, cracks on the sliding surface, and shear at the interface between the sliding layer and the back metal.

In Comparative Example 25, the temperatures of the upper cooling roll and the lower cooling roll were set at the same temperature in the production of the resin composition sheet. Accordingly, the fibrous particles in the entire sliding layer, that is both of the sliding surface side region and the interface side region of the sliding layer, were oriented substantially parallel to the sliding surface of the sliding layer and in the circumferential direction (the entire sliding layer corresponded to the interface side region), and thus falling off of the fibrous particles occurred and it is considered to have caused a large amount of wear of the sliding layer and cracks on the sliding surface.

In Comparative Example 26, the resin composition sheet was produced by injection molding. Accordingly, the fibrous particles in the sliding layer were dispersed in a non-oriented manner in the entire sliding layer. Thus, when a load of the shaft member was applied to the sliding layer, falling off of the fibrous particles occurred and it is considered to have caused a large amount of wear of the sliding layer and cracks on the sliding surface.

In Comparative Example 27, the fibrous particles in the entire sliding layer, that is both of the sliding surface side region and the interface side region of the sliding layer, were oriented substantially parallel to the sliding surface of the sliding layer and in the axial direction (the entire sliding layer corresponded to the sliding surface side region). Accordingly, the strength and resistance to deformation in the circumferential direction of the entire sliding layer was low and it is considered to have caused shear at the interface between the sliding layer and the back metal.

In Comparative Example 28, a thickness of the interface side region was 10% that is less than 15%, since a large temperature difference was made between the upper and the lower cooling rolls. Accordingly, the strength and resistance to deformation parallel to the sliding surface and in the circumferential direction was low and it is considered to have caused shear at the interface between the sliding layer and the back metal. 

The invention claimed is:
 1. A sliding member for a journal bearing, the sliding member comprising: a back-metal layer; and a sliding layer on the back-metal layer, wherein the sliding member has a partial cylindrical shape, wherein the sliding layer comprises a synthetic resin and fibrous particles dispersed in the synthetic resin at a volume ratio of 10 to 35% of the sliding layer, wherein the sliding layer includes a sliding surface side region including a sliding surface of the sliding layer and an interface side region including an interface between the sliding layer and the back-metal layer, the sliding surface side region contacts the interface side region, and a thickness of the interface side region is 15 to 50% of a thickness of the sliding layer, wherein the fibrous particles include a first set of fibrous particles in the sliding surface side region and a second set of fibrous particles in the interface side region, wherein, in the sliding surface side region, the first set of fibrous particles has a first average particle size D_(sur, axi) of 5 to 30 μm in view of an axial cross-section, and has a second average particle size D_(sur, cir) in view of a circumferential cross-section, and the second average particle size D_(sur, cir) is 5 to 20% of the first average particle size D_(sur, axi), wherein, in the interface side region, the second set of fibrous particles has a third average particle size D_(int, cir) of 5 to 30 μm in view of a circumferential cross-section, and has a fourth average particle size D_(int, axi) in view of an axial cross-section, and the fourth average particle size D_(int, axi) is 5 to 20% of the third average particle size D_(int, cir), wherein, in the sliding surface side region in view of the axial cross-section, at least one of the first set of fibrous particles has a length of a major axis not shorter than 20 μm, a volume ratio of the at least one of the first set of fibrous particles having the major axis length not shorter than 20 μm to a total volume of the first set of fibrous particles is not less than 10%, and a dispersion index of the at least one of the first set of fibrous particles having the major axis length not shorter than 20 μm is not less than 5, wherein, in the interface side region in view of the circumferential cross-section, at least one of the second set of fibrous particles has a length of major axis not shorter than 20 μm, a volume ratio of the at least one of the second set of fibrous particles having the major axis length not shorter than 20 μm to a total volume of the second set of fibrous particles in the interface side region is not less than 10%, and a dispersion index of the at least one of the second set of fibrous particles having the major axis length not shorter than 20 μm is not less than 5, and wherein the dispersion index is defined as an average of ratios X1/Y1 of the fibrous particles, where X1 represents a length of a fibrous particle in a cross-section in a direction parallel to the sliding surface, and Y1 represents a length of a fibrous particle in the cross-section in a direction perpendicular to the sliding surface.
 2. The sliding member according to claim 1, wherein, in the sliding surface side region of the axial cross-section, an average aspect ratio of the at least one of the first set of fibrous particles having the major axis length of not shorter than 20 μm is 1.5 to 10, and wherein in the interface side region of the circumferential cross-section, an average aspect ratio of the at least one of the second set of fibrous particles having the major axis length of not shorter than 20 μm is 1.5 to
 10. 3. The sliding member according to claim 1, wherein, in the sliding surface side region of the axial cross-section, the average aspect ratio of the at least one of the first set of fibrous particles having the major axis length of not shorter than 20 μm is 5 to 10, and wherein, in the interface side region of the circumferential cross-section, the average aspect ratio of the at least one of the second set of fibrous particles having the major axis length of not shorter than 20 μm is 5 to
 10. 4. The sliding member according to claim 1, wherein, in the sliding surface side region of the axial cross-section, the volume ratio of the at least one of the first set of fibrous particles having the major axis length of not shorter than 20 μm to the total volume of the first set of fibrous particles in the sliding surface side region is not less than 30%, and wherein, in the interface side region of the circumferential cross-section, the volume ratio of the at least one of the second set of fibrous particles having the major axis length of not shorter than 20 μm to the total volume of the second set of fibrous particles in the interface side region is not less than 30%.
 5. The sliding member according to claim 1, wherein the fibrous particles are composed of one or more of glass fiber particles, ceramic fiber particles, carbon fiber particles, aramid fiber particles, acrylic fiber particles, and polyvinyl alcohol fiber particles.
 6. The sliding member according to claim 1, wherein the synthetic resin is composed of one or more of polyether ether ketone, polyether ketone, polyether sulfone, polyamidimide, polyimide, polybenzimidazole, nylon, phenol, epoxy, polyacetal, polyphenylene sulfide, polyethylene, and polyetherimide.
 7. The sliding member according to claim 1, wherein the sliding layer further comprises one or more solid lubricants selected from graphite, molybdenum disulfide, tungsten disulfide, boron nitride, and polytetrafluoroethylene.
 8. The sliding member according to claim 1, wherein the sliding layer further comprises 1 to 10 volume % of one or more fillers selected from CaF₂, CaCo₃, talc, mica, mullite, iron oxide, calcium phosphate, potassium titanate, and Mo₂C.
 9. The sliding member according to claim 1, wherein the back-metal layer comprises a porous metal portion on a surface which is the interface between the back-metal layer and the sliding layer.
 10. A journal bearing comprising a plurality of the sliding members according to claim
 1. 